As molecular biology has helped to define regions of proteins that contribute to a particular biological activity, it has become desirable to synthesize short peptides to mimic (or inhibit) those activities. Many of the disadvantages encountered in therapeutic, diagnostic and industrial settings with purified proteins, or those produced by recombinant means, could easily be avoided by short synthetic peptides. For instance, synthetic peptides offer advantages of specificity, convenience of sample or bulk preparation, lower relative cost, high degree of purity, and long shelf-life.
Despite the great promise of synthetic peptides, the technology remains, to a large extent, a laboratory tool. Precise sequence and binding data are not available for most proteins of significant medical, agricultural or industrial interest. Even when the sequence of a protein is known, the process of identifying short sequences which are responsible for or contribute to a biological activity may be extremely tedious, if not nearly impossible in many instances.
Thus, the ability to generate and efficiently screen very large collections of peptides for desired binding activities would be of enormous interest. It would enable the identification of novel agonists and antagonists for receptors, the isolation of specific inhibitors of enzymes, provide probes for structural and functional analyses of binding sites of many proteins, and ligands for many other compounds employed in a wide variety of applications.
The generation of large numbers of peptide sequences by the cloning and expression of randomly-generated mixtures of oligonucleotides is possible in the appropriate recombinant vectors. See, e.g., Oliphant et al., Gene 44:177-183 (1986). Such a large number of compounds can be produced, however, that methods for efficient physical and genetic selection are required. Without such methods the usefulness of these large peptide libraries in providing ligands of potential interest may be lost. The present invention provides methods for efficient screening and selection from a large peptide library, fulfilling this and other related needs.